A printing head for an ink jet printer may be divided into two parts, i.e. a pump chamber plate and a capillary plate. However, if this construction is selected it is important that the plates are secured together in such a manner that there is no danger of leakage at the abutment between the two plates. If leakage occurs between the plates there is a real risk not only that ink may leak out but that air will penetrate into the pump chambers. If air finds its way into the pump chambers then the entire printing head may be rendered unusable since the reduction of volume in one pump chamber would not develop enough pressure to eject the desired quantity of ink, thereby causing partial or entire failure of ink jet printing due to air compression in the pump chamber.
In co-pending U.S. patent application Ser. No. 557,228, the capillary part is of such a shape that the inlet for each capillary channel is adjacent to an edge as well as to a large surface of the plate. This arrangement results in an unnecessarily complicated sealing problem.
It is therefore an object of the present invention to provide a capillary part in a capillary plate that can be reliably sealed in a printing head by a comparatively simple means.
An object of the present invention is to provide a printing head for an ink jet printer in which each channel in the second or capillary plate, at its broadest portion, opens into one short side of the plate, and the capillary tube connected to the channel opens into the opposite short side of the plate. Thus, by making the inlets and outlets of the channels in opposite sides of the capillary plate, the majority of the sealing problems with respect to the printing head have been eliminated. This is so because sealing is now required only on one surface. A reliable sealing can be accomplished in any suitable manner, for example, by gluing or ultrasonic welding.